A fluid, whether gaseous or liquid, may flow through a conduit or duct. The fluid may be propelled by a pressure creating device, such as a compressor or other type of pump. One type of compressor used to propel fluid, particularly gas, is a reciprocating compressor. Effective control of the pressure pulsations generated by reciprocating compressors is desirable to prevent damaging shaking forces and stresses in system piping, vessels, and mechanical equipment and structures, as well as to prevent detrimental time-variant suction and discharge pressures at the compressor cylinder flanges. The pressure and flow delivered by reciprocating compressors varies throughout the stroke of each compressor cylinder piston, thus creating pressure variations over time.
A reciprocating compressor may have a piston that is moved alternately toward one end of a cylinder and then to an opposing end of the cylinder and fluid may be propelled from the cylinder by the piston in either one or both directions of piston movement. Reciprocating compressors may use single-acting pistons or double-acting pistons. The double-acting pistons compress gas at the discharge of the compressor using both strokes of the piston. Exemplary double-acting compressors are those manufactured by Ariel Corporation of Mount Vernon, Ohio. The pumping action of each single-acting or double-acting piston creates complex cyclic pressure waves. The pressure waves of a double-acting piston generally have a primary frequency at twice the compressor operating speed with many harmonics. Variations in pressure within conduits and ducts created by such pumping actions are commonly referred to as pulsations.
To reduce the amplitude of the pressure waves upstream and downstream of the compressor, which could otherwise excite system mechanical natural frequencies, overstress system elements and piping, and interfere with meter measurements, it has been customary to dampen the pressure waves through the use of expansion volume bottles, choke tubes, orifices, baffles, etc. These devices are used singly or in combination to dampen pressure waves and reduce the resulting forces. However, those approaches generally result in significant system pressure losses on both the suction and discharge sides of the compressor, reducing compressor efficiency and flow capacity. Since the flow is pulsating as it moves into and out of the compressor, the amount of pressure drop typically increases with the amplitude of the pulsation.
Pressure pulsations may be controlled with a system of primary and/or secondary volume bottles, often with complex internal choke tubes, baffles, and chambers, as well as various orifice plates installed at specific locations in the system piping. These devices accomplish pulsation control by adding resistance, or damping, to the system, and they result in pressure losses that may exist both upstream and downstream of the compressor cylinders. For common pipeline transmission applications, particularly those having low pressure ratios, such as natural gas pipeline systems, pressure losses can noticeably degrade system operating efficiency. As larger high-speed compressors have been increasingly applied to pipeline transmission applications, these influences are thought to have become more detrimental to performance, due to the higher frequency pulsations that must be damped. In extreme cases in the field, traditional methods of pulsation control have been reported to add 20 percent or more to the driver horsepower requirements for high-speed, low-ratio compressors.
An investigation of a new tuning technology that involves cancellation of pulsations, rather than dampening, has been undertaken to assess its potential use for the design of reciprocating gas compressor systems. Simulations predict that this new pulsation attenuation technology can control pulsations to 1.0 percent peak-to-peak over a reasonable speed range with less than 0.1 percent overall system pressure drop.
Study has been made as to the effect of the use of differing length parallel tubes to cancel sounds of a particular wavelength. Acoustic wave interference in pipes was studied in 1833 by Herschel, who predicted that sound could be canceled by dividing two waves from the same source and recombining them out of phase after they followed paths of different lengths. Experiments by Quincke in 1866 verified that Herschel's system did suppress sound.
Variations on the Herschel-Quincke solutions have been proposed including a method for controlling exhaust noise from an internal combustion engine by using bypass pipes such as shown in U.S. Pat. No. 6,633,646 to Hwang (hereinafter “Hwang”) See FIG. 1 and FIG. 5. In such an apparatus, a main exhaust pipe is provided with two U-shaped bypass pipes through which the exhaust passage of the main pipe is partially diverted before being reintegrated. With such a construction, the phase difference between the main noise components of the exhaust gas passing through the fixed pipe and the noise components of the exhaust gas passing through the first bypass pipe is adjusted 180 degrees, thus suppressing the main noise component and its odd harmonics. The length of the second bypass pipe is adjusted so that the noise component having a frequency of two times the frequency of the main noise component is suppressed. However, the above method does not effectively attenuate the 4th harmonic, i.e., the noise component having a frequency four times the main noise component, nor any other harmonics divisible by 4. Such an arrangement furthermore operates on a single primary frequency and certain of its harmonics and so is unlikely to provide effective noise attenuation over a range of noise frequencies. Furthermore, Herschel, Quincke, and Hwang directed their efforts toward sound attenuation, not pulsation attenuation. While attenuation of sound and pulsations may be achieved by similar means, they operate differently by degrees to achieve different results. For example, reduction of sound is frequently directed to human comfort and reduction of high frequency wavelengths that are bothersome to human beings. Conversely, pulsation reduction frequently focuses on reducing low frequency wavelengths that may cause damage to mechanical systems, such as pipes, conduits, ducts, mechanical equipment and structures, sometimes in critical safety applications such as natural gas pipelines.
Thus, certain embodiments of the present pulsation attenuation apparatuses and methods attenuate pulsations in a conduit or duct. While sound wave propagation cancellation and pulse propagation cancellation may be based on some of the same principles, it should be recognized by one skilled in the art of wave dynamics that reduction of sound wave propagation has a different goal and operates differently from reduction of pulse propagation.
Certain embodiments of the present pulsation attenuation apparatuses and methods may further preserve the integrity of piping and vessel systems subjected to pulsations and certain embodiments of the present pulsation attenuation apparatuses and methods may increase flow of a fluid through such systems.
Embodiments of the inventions described herein reduce pulsations in pumping systems, including pumping systems utilizing reciprocating compressors and rotary pumps (collectively referred to herein as “pumps”).
Embodiments of the inventions described herein reduce energy consumption when compared with existing systems.
Embodiments of the inventions described herein increase flow in pumping systems when compared to existing systems.
Embodiments of the inventions described herein reduce the pressure differential against which pumps operate.